The large part of this proposal is concerned with identification of the catalytic residues of aldehyde dehydrogenase (EC 1.2.1.3) by chemical modification employing group specific, affinity and suicide reagents. The chemical modification of the active site will, in addition to increasing knowledge, provide means for designing specific inhibitors or activators of the individual isozymes, thus providing grounds for development of therapeutic agents useful for treatment of the alcoholic. Purification and characterization of other isozymes will increase our understanding of physiological roles of individual isozymes. Characterization will include: amino acid analysis, molecular weight of the isozymes and their subunits, peptide mapping, interaction with antibodies, substrate and coenzyme specificity and kinetic properties with acetaldehyde as substrate. Concurrently, aldehyde dehydrogenase content and isozyme distribution in crude extracts of different human tissues (post-mortem) from alcoholics and non-alcoholics will be investigated and isozymes from post-mortem liver of a diagnosed alcoholic will be purified for comparison with normal isozymes. Knowledge of the properties of human aldehyde dehydrogenase isozymes should lead to a better understanding of alcoholism in several ways. Delineation of the enzyme's catalytic properties could throw light on the physiological roles of individual isozymes, as well as identify the isozyme for which acetaldehyde and catecholamine metabolites compete. Physicochemical properties and stability studies will also facilitate interpretation of how these isozymes can be inactivated in vivo. Inhibition studies can establish mechanisms of drug action and help to design drugs useful for prevention and treatment. Comparison of isozymes from alcoholics with those from normal individuals may also help in interpreting other research on alcoholism (e.g., genetic factors in alcoholism, fetal alcohol syndrome and alcoholism in women).